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Greetings from San Diego.

I have done my fair share of synchrotron data collection on many diverse macromolecular crystal systems.  But this weekend was the first time that I ever shot crystals that failed to diffract entirely.

Details:  we have purified and crystallized an ~90 kDa proteolytic fragment containing a single point mutant version of a myosin motor domain in complex with a separate light chain polypeptide.  The crystals are relatively small (10-30 microns in each dimension) but clearly crystalline in character (clear faces, edges, and facets).  The crystals tested positive for protein by absorbance at 280 nm.  This weekend we tested more than 40 of them for diffraction in different cryo solvents and did not observe a single identifiable diffracted ray.  It was as if we had only cryo on the end of our loops.  Increasing the time of exposure or annealing did nothing to improve the situation.  Crystals from a different protein system that we also tested this weekend on the same beamline diffracted to beyond 1.3 Å.

I only post this because, in my experience, crystals of this size and superficial quality always give some signal--even if it is horrifyingly bad.  But never complete diffraction silence.  We will work this week to identify what it is that we "crystallized".  But can anybody who has had a similar experience suggest what it is that could be going on here?

Thanks in advance for any responses.  And happy holidays to us all.

Tom Huxford.

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